全文获取类型
收费全文 | 1210篇 |
免费 | 34篇 |
国内免费 | 5篇 |
专业分类
化学 | 813篇 |
晶体学 | 1篇 |
力学 | 45篇 |
数学 | 214篇 |
物理学 | 176篇 |
出版年
2023年 | 6篇 |
2019年 | 11篇 |
2018年 | 14篇 |
2017年 | 11篇 |
2016年 | 24篇 |
2015年 | 28篇 |
2014年 | 27篇 |
2013年 | 62篇 |
2012年 | 52篇 |
2011年 | 44篇 |
2010年 | 27篇 |
2009年 | 32篇 |
2008年 | 47篇 |
2007年 | 47篇 |
2006年 | 41篇 |
2005年 | 38篇 |
2004年 | 40篇 |
2003年 | 36篇 |
2002年 | 52篇 |
2001年 | 15篇 |
2000年 | 20篇 |
1999年 | 17篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 13篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 15篇 |
1992年 | 20篇 |
1991年 | 12篇 |
1990年 | 20篇 |
1989年 | 7篇 |
1988年 | 21篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 29篇 |
1982年 | 24篇 |
1981年 | 16篇 |
1980年 | 28篇 |
1979年 | 21篇 |
1978年 | 24篇 |
1977年 | 22篇 |
1976年 | 32篇 |
1975年 | 13篇 |
1974年 | 13篇 |
1973年 | 10篇 |
1972年 | 9篇 |
1971年 | 7篇 |
排序方式: 共有1249条查询结果,搜索用时 359 毫秒
81.
82.
Maud Jenart Claude Niebel Jean-Yves Balandier Julie Leroy Alix Mignolet Sara Stas Antoine Van Vooren Jérôme Cornil Yves Henri Geerts 《Tetrahedron》2012,68(1):349-355
Two quaterthiophene-based dimers including an ethylene bridge have been designed and efficiently prepared; experimental and computational studies show a promising potential as semiconducting material with a charge transport of higher dimensionality compared to quaterthiophene. 相似文献
83.
84.
Aurica Farcas Giulia Tregnago Ana‐Maria Resmerita Sarah Taleb Dehkordi Sophie Cantin Fabrice Goubard Pierre‐Henri Aubert Franco Cacialli 《Journal of polymer science. Part A, Polymer chemistry》2014,52(4):460-471
The photophysical properties of two polyrotaxanes ( PFBTh?PSβCD and PFBTh?PMeβCD ) composed of fluorene and bithiophene encapsulated into permodified β‐cyclodextrin cavities have been investigated and compared with those of the reference PFBTh . Rotaxane formation results in improvements of the thermal stability, solubility in common organic solvents, as well as better film forming ability combined with a high transparency. As expected PFBTh and its encapsulated forms absorb at wavelengths beyond 510 nm, and time‐resolved photoluminescence (PL) in solution shows a well‐define vibronic structures with a predominance of the 0‐0 transitions and an energy difference of 0.16 eV. The fluorescence lifetimes follow a monoexponential decay with a value τ = 630 ± 30 ps. Atomic force microscopy, AFM, indicated a tendency of polyrotaxanes to organize into fibers. The advancing contact angles indicated higher surface hydrophobicity and lower surface free‐energy values for polyrotaxanes compared with their unthreaded analogues. The device based on PFBTh?PSβCD: PCBM in a 1/1 w/w ratio under simulated AM 1.5G illumination at 100 mW cm?2 exhibited improved photovoltaic parameters of cells, resulted in high Voc (0.68 V), Jsc (1.65 mA cm?2), FF (31.6%), and PCE (0.35) values, compared with PFBTh or PFBTh?PMeβCD , respectively. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 460–471 相似文献
85.
Michèle Postel Félix Tomi Henri Li Kam Wah Laurence Mordenti Patricia Guillaume 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):453-457
Abstract Fe(NO)2XL and Fe(NO)X2L nitrosyl iron complexes, X = Cl, I, and L = HMPA, dppe, PPh3, activate molecular O2 to yield nitrato complexes. The phosphorous ligand is decisive for the oxidative power of these nitrates: with HMPA or dppe, oxygen transfer occurs only to phosphines. On going from HMPA to PPh3 the single nitrato complex obtained, Fe(NO)2X(OPPh3)2 selectively epoxidizes cyclohexene, and this is the first example of oxygen transfer from a nitrato ligand to an olefin. 相似文献
86.
Henri J.-M. Dou Parina Hassanaly Jacky Kister Jacques Metzger 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):355-358
Abstract Alkylation via phase transfer catalysis of several ambident anions of the |N–C–S|? type leads exclusively to S-substitution. Yields obtained are better or equal to those given by conventional methods and experimental work-up is very much simplified compared to the latter. 相似文献
87.
88.
We introduce a method for change detection under nonuniform changes of intensity using an improved least-squares method. A locally adaptive normalizing window is correlated with the two images, and a morphological postprocessing is then applied to isolate objects that have been added or removed from the scene. We use a modification of the least-squares solution to get rid of clutter caused by intensity changes that do not satisfy the model assumed for the least-squares solution. 相似文献
89.
Generalizations and Properties of the Principal Eigenvalue of Elliptic Operators in Unbounded Domains
下载免费PDF全文
![点击此处可从《纯数学与应用数学通讯》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Using three different notions of the generalized principal eigenvalue of linear second‐order elliptic operators in unbounded domains, we derive necessary and sufficient conditions for the validity of the maximum principle, as well as for the existence of positive eigenfunctions for the Dirichlet problem. Relations between these principal eigenvalues, their simplicity, and several other properties are further discussed. © 2015 Wiley Periodicals, Inc. 相似文献
90.